This invention relates to apparatus and a method for identifying measuring or detecting gas or liquid borne substances which may be gases, vapours, liquids or solids.
Several attempts have been made to construct a device which can sense and distinguish various gases and vapours, such devices being of potential importance in the food and drink industries, in the analysis of perfumes, and in diagnostic medicine, amongst other uses. These devices have used sensors which respond to a variety of gases, liquids or particulate solids (such as solids present in smoke), but have predominantly been operated in environments where a particular class of chemical is to be detected, in each case the chemical being the only substance in the relevant environment to which the sensor is sensitive. It is also known to use sensors which respond to one specific compound class. However, in recent years there have been proposals for a device thought to be modelled on the mammalian nose, having a plurality of sensors which are each responsive to a wide variety of chemicals, but which respond differently from each other to those chemicals. By monitoring the outputs of the sensors together, it is possible to identify substances from the pattern of the outputs. The effect of varying concentrations can be largely avoided by monitoring the relative magnitudes of the sensor outputs, for example by analysing the ratios of pairs of outputs. A device of this form is outlined in a paper by Persaud and Dodd in `Nature`, Volume 299 at page 352 (Sept. 23, 1982). One of the main drawbacks of the approach adopted by Persaud and Dodd is the complexity of the pattern recognition process when the outputs of several sensors are to be analysed, and it is an object of the present invention to provide apparatus and a method which allow simpler analysis.